OXYMETRY DEEP IN TISSUES WITH LOW-FREQUENCY ELECTRON-PARAMAGNETIC-RESONANCE

We have measured the oxygen concentration in the body water of murine FSa and NFSa fibrosarcomas using a new method for quantitative oxygen concentration determination deep in the tissues of a living animal. Th e measurement uses unusually low-frequency electron paramagnetic spect roscopy sensitive to substrate 7 cm deep in tissue, partially deuterat ed spin probes (spin labels of molecular mass 195, approximating that of glucose) whose distribution compartment can be targeted with facile adduct substitution, and novel analytic techniques. We show that the water-compartment oxygen concentration of the tumors decreases as the tumor size increases and also shows a trend to decrease as radiobiolog ic hypoxia increases. An oxymetric spectral image of the tumor is pres ented. The technique will improve with larger human tissue samples. It provides the potential to quantitatively assess tissue hypoxia in isc hemic or preischemic states in stroke and myocardial infarction. It wi ll allow direct assessment of tumor hypoxia to determine the usefulnes s of radiation and chemotherapy adjuvants directed to hypoxic cell com partments.